Air is about 1.3 g/liter, helium is 0.17. You'd save about 1.1 grams per liter of volume.
Text with the video says the weight advantage is 3 ounces...that's 84 grams. The fuselage would have to be, roughly, 75 liters in volume to save that three ounces. That's about eighteen gallons... a bit bigger than a standard kitchen bag.
Probably doable, though there's probably an external keel on the fuselage and none of the electronics inside. It'd be sporty keeping the fuselage stiff (helium loves to leak) but for a ~3 minute flight demonstration probably acceptable.
Question is, did the REST of the structure have to be boosted to accommodate the inflated fuselage. The weight delta may not have been that significant.
Ron Wanttaja